A switch power supply is used to supply power to a mobile electronic device such as a cell phone and a laptop. The switch power supply has an advantage of small volume, high efficiency and high precision for a constant voltage and the like.
Nowadays, with the development of mobile electronic devices and more attention given to saving energy and protecting the environment, a higher requirement for performance (such as no-load power consumption and dynamic load response speed) of the switch power supply is proposed such that a continuous improvement on a constant voltage control mode for an integrated circuit of the switch power supply is conducted by developers to obtain a better constant voltage control mode to solve current problems of the switch power supply. The constant voltage control mode for the integrated circuit of the switch power supply includes a primary constant voltage control mode and a secondary constant voltage control mode.
Since there are some errors and limitations in taking a sample of an output voltage of the switch power supply coupled to a feedback winding in the primary constant voltage control mode, the current output voltage of the switch power supply cannot accurately be obtained in real time, such that the performance (such as the dynamic load response speed) of the switch power supply is poor in the primary constant voltage control mode and either the no-load power consumption or a no-load working frequency of the switch power supply in the primary constant voltage control mode cannot be controlled to be low. Furthermore, although the switch power supply has a good performance on the dynamic load response in the secondary constant voltage control mode, the power consumption is high caused by the fact that some feedback signals in the secondary constant voltage control mode are analog signals, and thus the no-load power consumption of the switch power supply in the secondary constant voltage control mode also cannot be controlled to be low.